1. Field of the Invention
The present invention relates to a spindle motor and more specifically to a spindle motor for use in a storage disk drive.
2. Description of the Related Art
Motors including a bearing mechanism using fluid dynamic pressure have often been used in storage disk drives. A spindle motor disclosed in JP-A 2009-136143 includes a fixed shaft, an annular bearing component, a rotor component, and an annular cover. The bearing component is arranged on an upper end portion of the fixed shaft. The bearing component is integrally provided with the fixed shaft. The rotor component is arranged radially outward of the fixed shaft. The annular cover is arranged above the bearing component. A radially outer end portion of the annular cover is adhered to an upper end portion of the rotor component. An outer circumferential surface of the bearing component is arranged opposite an inner circumferential surface of the upper end portion of the rotor component. A seal gap is defined between the outer circumferential surface of the bearing component and the inner circumferential surface of the upper end portion of the rotor component. The seal gap is covered by the annular cover. Paragraph [0043] of JP-A 2009-136143 states: “The annular cover 330 defines a labyrinth seal 348 arranged to additionally seal the seal gap 332 together with an upper end surface of the bearing component 318.”
Another conventional dynamic pressure fluid bearing apparatus included in a spindle motor is disclosed in JP-A 2007-162759. This conventional dynamic pressure fluid bearing apparatus includes a shaft body and a tubular sleeve body inside which the shaft body is inserted. The shaft body is fixed to a base plate of the motor. The sleeve body is fixed to a rotor of the motor. The shaft body is provided with a first thrust flange and a second thrust flange. The first thrust flange and the second thrust flange are both annular and are arranged on an upper side and a lower side of the sleeve body, respectively. In the dynamic pressure fluid bearing apparatus, a radial bearing portion is defined between the shaft body and the sleeve body, and a thrust bearing portion is defined between each of the two thrust flanges and the sleeve body. In addition, the sleeve body includes communicating holes defined therein to provide communication between two thrust gaps. Tapered seal portions are defined in the vicinity of upper and lower end openings of the communicating holes.
Another example of a known fluid dynamic bearing motor is disclosed in U.S. Pat. No. 6,991,376. This fluid dynamic bearing motor includes a shaft, a top plate, a bottom plate, and a hub. The top plate is fixed to an upper end of the shaft and the bottom plate is fixed to a lower end of the shaft. The hub is arranged between the top plate and the bottom plate, and is supported so as to be rotatable with respect to the shaft. The hub includes a recirculation channel extending therethrough defined therein. An upper portion of the hub includes a projecting portion arranged radially outward of an outer edge portion of the top plate. A capillary seal is defined between the projecting portion and the outer edge portion of the top plate. A lower portion of the hub includes another projecting portion arranged radially outward of an outer edge portion of the bottom plate. A capillary seal is also defined between the other projecting portion and the outer edge portion of the bottom plate. The influence of a pressure gradient of a lubricating oil in each of the capillary seals is minimized by the recirculation channel being arranged radially inward of the capillary seals.
In some motors, a cap member is arranged in a rotating portion to cover a seal gap. The motor described in JP-A 2009-136143 is an example of one of these motors. In such a motor, there is a gap between the cap member and a component of a stationary portion which defines the seal gap, and this gap may permit an evaporated lubricating oil to pass therethrough to an outside of the motor. Moreover, an attempt to ensure sufficient rigidity of the cap member by increasing the thickness of the cap member leads to a failure to reduce the overall thickness of the motor. Moreover, a reduction in the thickness of the cap member may result in a reduction in the precision with which the cap member is shaped, and may lead to a contact of the cap member with the stationary portion during rotation of the motor.
In the motor disclosed in JP-A 2007-162759, a difference in pressure between the upper tapered seal portion and the lower tapered seal portion is large because of the large axial distance between a surface of a lubricating oil in the upper tapered seal portion and a surface of the lubricating oil in the lower tapered seal portion. Therefore, when the motor is oriented in a variety of directions, the surface of the lubricating oil in each tapered seal portion will fluctuate greatly. Because of this, it is necessary to provide a complicated design to prevent a leakage of the lubricating oil.
Similarly, with respect to the motor disclosed in U.S. Pat. No. 6,991,376, a difference in pressure between the upper capillary seal and the lower capillary seal is large because of the large axial distance between a surface of the lubricating oil in the upper capillary seal and a surface of the lubricating oil in the lower capillary seal.